Study On Structure And Properties Of Sol-gel Bioactive Glass And Molecular Dynamics Simulation

In recent years,sol-gel bioactive glass has attracted extensive attention in the field of biomaterials and medicine because of its excellent biocompatibility and bioactivity.Studies have shown that the most representative sol-gel bioactive glass:58S shows excellent tissue regeneration and repair performance in the treatment of bone,tooth and skin wounds,and is a new type of silicon-based amorphous biological material with good application potential and research value.The bioactivity of materials largely depends on the release process of its constituent substances in the form of ions or ionic groups in the physiological environment,which in turn is directly related to the structure form of random network of materials.Therefore,a prerequisite for direct prediction of the bioactive reactions of glass is a correct understanding of the composition of the glass components at the atomic level.Over the past 20 years,researchers have used a variety of 58S and biological methods to study the mechanism of biological cells and tissues in terms of material structure,but,because of the limitations on time for amorphous materials detection technology,unable to analyze the structure of the atomic level,allowing the researchers to from material on the nature of the structure shows good biological activity as well as a variety of special phenomena in histology,cell biology,a reasonable explanation.The Molecular Dynamics（MD）simulation technology used in this study can study 58S structure from the atomic level to understand the relationship between its structure and performance,so as to provide theoretical support for its in-depth research in the direction of gene activation and promotion of tissue regeneration and repair.It provides reference for the research and development of new silicon-based tissue regeneration and repair materials.In this study,the structure and properties of 58S material were analyzed theoretically by means of material preparation and structure analysis research technology,and MD simulation technology.First,58S was prepared and its bioactivity was verified.Then,the microstructure and surface structure were tested and analyzed by magic Angle rotating NMR,Raman,X-ray surface photoelectron spectroscopy and other techniques,and the new 58S structure features were obtained.Then,based on the MD principle,58S was simulated by LAMMPS.Through Python programming and experimental test analysis,some new insights on the relationship between structure and performance were obtained,and the relationship between its microstructure,surface structure and bioactivity were deeply analyzed.Finally,the diffusion properties of 58S were studied,and the relationship between network modifiers and bioactivity was further studied.The main research work and results are as follows:（1）The experimental results show that the prepared 58S has excellent bioactivity,and the network and surface structure of the prepared 58S was analyzed in depth.It was found by Raman spectra that the-Si-O-Si-O-minimum ring connections were mainly four-membered and five-membered rings,and combined with NMR deconvolution,it was determined that the Si and P in the network structure were mainly Q³_Si connections,accounting for 54.87%,and Q_P¹ connections,accounting for 84.60%.Moreover,X-ray surface photoelectron spectroscopy and other tests showed that the surface of 58S without being submerged in the simulated body fluid had produced some silicon hydroxyl and hydroxy carbonate apatite（HCA）crystals.（2）MD simulation 58S was successfully realized by combining Teter and ZBL potential function,and the optimal simulation temperature was determined as 3000 K,the cooling rate was 1 K/ps,the time step was 1 fs.The simulated structure is consistent with the experimental trend,and the fragmentation network structure of Q³_Si is the main structure,P is mainly Q_P¹structure,and there is Si-O-P connection,easy hydrolysis in solution,which can promote the bioactivity.The microstructure analysis shows that Ca²⁺does not form stable coordination,which is conducive to its release from the network.The P-O bond tends to the lowest energy state,and the Ca²⁺around PO₄^3-is obviously more than that around silicon oxygen tetrahedron,which reduces the ion transport energy during mineralization,and provides favorable conditions for the rapid formation of HCA and increases the bioactivity.（3）Through the analysis of surface structure and diffusion properties,the number of non-bridged oxygen near the surface of 58S bulk is obviously more than bridged oxygen,which is conducive to the formation of a large number of silicon hydroxyl groups on the surface.In addition,according to the self-diffusion coefficient calculated by the Mean square displacements,the diffusion activation energy of Ca²⁺is 0.664 e V,which is easy to diffuse from the network,and Ca²⁺which is close to PO₄^3-is easy to combine with CO₂ and H₂O in the air to form HCA,so as to produce strong bioactivity.To sum up,based on the research results,a biological activity reaction hypothesis was proposed in this paper.The four-membered ring of 58S in the air began to break,destroying part of the annular structure.After contact with the solution,the hydrolytic fracture of the three and four-membered rings in the embedded ring gradually damaged the larger annular structure,making it become a chain.Non-bridged oxygen rapidly forms silicon hydroxyl group,and the unhydrolyzed silicon oxygen chain is equivalent to the skeleton,which acts as the support of the gel layer,making it more stable and uniform,and generating a continuous strong adsorption force.In the structure,the unstable Si-O-P prefer to hydrolyze,and the free PO₄^3-was produced by breaking the bond.At the same time,the non-bridging oxygen also formed silicon hydroxyl group.Then,the structure hydrolyzes gradually from the surface to the interior to form a thick and uniform gel layer.The gel layer close to the 58S bulk mainly attracts Ca²⁺and PO₄^3-from the material,and the gel layer in contact with the solution attracts Ca²⁺and PO₄^3-from the solution.This can form a thicker and stable layer of HCA,increasing the ability of bone bonding.In this paper,the idea and method of in-depth study of 58S structure through molecular dynamics simulation combined with experimental testing are described,and the relationship between 58S structure and bioactivity is discussed in detail,which provides basic theoretical support and new methods for explaining and guiding the design of new bioactive glass.